1. Technical Field
The present invention relates to an optical position measuring arrangement for determining the relative position of a fiber-optical scanning head and of a measuring graduation which can be moved with respect to it in at least one measuring direction.
2. Background Information
Customarily, known optical position measuring arrangements include a measuring graduation, as well as a scanning unit, which can be moved in relation to it. As a rule, a light source, optoelectronic detector elements, as well as further optical components, such as lenses, gratings, etc. are arranged in the scanning unit. However, in certain cases of application a scanning unit having all these components can possibly be of too large a size. Furthermore, in connection with certain applications the result can be undesired effects on the active components of such a scanning unit by electromagnetic interference fields or increased temperatures. Moreover, a thermal effect on the measuring accuracy can occur because of the dissipation of electrical power, in particular that of the light source.
Therefore solutions for optical position measuring arrangements have become known, in which only the scanned measuring graduation, as well as a passive fiber-optical scanning head which can be moved in relation to it, are arranged at the actual measurement location. The remaining active components relative to the functioning of the scanning process, such as the light source, optoelectronic detector elements, etc. are arranged spatially distant from the measurement location and are connected with the fiber-optical scanning head by fiber-optical waveguides. It is possible in this way to realize a system of an extremely compact size at the actual measurement location. It is furthermore also possible to minimize interference effects on the various active components on the scanning site.
Such a position measuring arrangement is known from U.S. Pat. No. 6,906,315, for example, the entire contents of which are incorporated herein by reference. The position measuring arrangement disclosed in this publication includes, besides a measuring graduation embodied as a linear reflection measuring graduation, a fiber-optical scanning head, which can be displaced relative to it in at least one measuring direction. An electronic follow-up device is arranged, spatially distanced, downstream of the fiber-optical scanning head and is connected with it by means of suitable fiber-optical waveguides. Here, the electronic follow-up device includes, inter alia, the light source required for optical scanning, several optoelectronic detector elements, as well as further active components for signal generation and further signal processing, as required. The fiber-optical scanning head substantially includes the ends of several fiber-optical waveguides for supplying illumination, as well as for returning the signal-generating light beam bundles. At their ends on the measuring graduation side, the fiber-optical waveguides used for returning the light beam bundles are provided with suitable scanning gratings and are used for generating position-dependent, phase-shifted quadrature signals, i.e. for example four quadrature signals, each phase-shifted by 90°. In a known manner, the scanning gratings with different signal phases have suitable geometric offset distances between each other for this purpose.
With this solution it is considered to be disadvantageous that no so-called single field scanning of the measuring graduation is possible by it. This is understood to be scanning in which all phase-shifted signal portions are generated out of the same field of the scanned measuring graduation. It is a special advantage of this type of scanning that it is relatively insensitive to dirt on the measuring graduation and, in case of possible dirt accumulation, basically all phase-shifted signal portions are evenly affected. It is possible by this to minimize errors in the course of further signal processing, i.e. during a subsequent signal interpolation, for example.